United find themselves 12 points behind Manchester City in the Premier League title race with 15 games to go. But rather than simply offering a mid-season boost, Mourinho says Sanchez -- should he sign -- is a player capable of taking United to the next level.

He said: "The team is lacking nothing. It is not the point of lacking something or we desperately need something. It is just thinking about the improvement of the team in the future.

"If it happens, it happens, and we are sure that it is for the good of the future of the team. If it doesn't happen, it doesn't happen."

Mourinho admits doing transfer business in January usually hints that a club has made mistakes in the summer. But the Portuguese coach insists that is not the case with United's pursuit of Sanchez, and that the chance to sign the 29-year-old was too good an opportunity to turn down.

Alexis Sanchez is on the verge of joining Manchester United from Arsenal.

He added: "I think the idea of the transfer market in midseason, normally I say that is to help clubs that didn't work well in the summer.

"I think that's for me the point of the January transfer window, is to help the clubs that didn't work well in the summer and they feel they have to do something in January to help what they didn't do well before.

"It's because of that we don't like to do in January because it shows that we didn't give our best, we didn't try our best and we don't like to do it.

"But if you have the chance to do some special players, some player in special circumstances, some player that you do in the summer and you have the chance to do it now.

"That's a special situation and you try to do it. It's as simple as that."

Sources have told ESPN FC that Sanchez is expected to sign a four-and-a-half year deal at Old Trafford once negotiations have been concluded.

There is hope he could make his debut in the FA Cup fourth-round tie with Yeovil Town on Friday night, before a Premier League debut against Tottenham at Wembley on Jan. 31.

Mourinho hinted Sanchez's signing would remove the need to buy another attacker in the summer, allowing the board to instead focus on a defender and a midfielder.

He said: "If we have in our mind in the summer to improve the team in two or three positions, basically to improve the team in all the departments, if you have the chance to do something now it means that you don't do in the summer.

"Another thing is we get one or two players just to improve a little bit the squad and then in the summer you are going to do it again. No.

"In the summer, we would probably have three transfers to do. If we do one now, in the summer it is three minus one."

Rob is ESPN FC's Manchester United correspondent. Follow him on Twitter @RobDawsonESPN.